GuardShield™ Type 2 Safety Light Curtain Installation Instructions
6
Original instructions
Determining the Safety Distance
The light curtain must be mounted with proper safety distance
• From the point of danger
• From reflecting surfaces
US Safety Distance Formula
This distance, referred to as the safety distance, must be properly
calculated prior to determining the safety light curtain protective height
and mounting the light curtains on the machine. Failure to properly
calculate this safety distance may result in operator injury.
In the United States there are two formulas that are used to properly
calculate the safety distance. The first, the OSHA formula, is the
minimum requirement for the calculation of the safety distance. The
second formula, the one recommended by Rockwell Automation, is the
ANSI formula, which incorporates additional factors to be considered
when calculating the safety distance.
OSHA Safety Distance Calculation Formula
The OSHA safety distance formula as specified in CFR Subpart O
1910.217 is as follows:
Ds = 63 X TS
Ds Safety Distance
63 Is the OSHA recommended hand speed constant in inches
per second
Ts Is the total stop time of all devices in the safety circuit,
measured in seconds. This value must include all
components involved in stopping the hazardous motion of
the machinery. For a mechanical power press it is the
stopping time measured at approximately the 90º position of
the crankshaft rotation.
Note: The TSnumber must include the response times of all
devices, including the response time of the safety light
curtain, the safety light curtain controller (if used), the
machine’s control circuit and any other devices that react to
stop the hazardous motion of the machinery. Not including
the response time of a device or devices in the stop time
calculation will result in insufficient safety distance for the
application. This may result in operator injury.
The ANSI Safety Distance Formula
The ANSI safety distance formula, which is the Rockwell Automation
recommended formula, is as follows:
DS= K x (TS+ TC+ Tr+ Tbm) + Dpf
Ds Minimum safety distance between the safe guarding device
and the nearest point of operation hazard, in inches.
K Hand speed constant in inches per second. The ANSI
standard value is 63 inches per second when the operator
begins reaching toward the point of operation hazard from
rest. NOTE: ANSI B11.19 1990 E4.2.3.3.5 states “The
value of the hand speed constant, K, has been determined
by various studies and although these studies indicate speeds
of 63 inches/second to over 100 inches/second, they are
not conclusive determinations. The employer should
consider all factors, including the physical ability of the
operator, when determining the value of K to be used.”
Ts Stop time of the machine tool measured at the final control
element.
Tc Response time of the control system
Note: Tsand Tcare usually measured by a stop time measuring
device.
Tr Response time of the presence sensing device (safety light
curtain) and its interface, if any. This value is generally stated
by the device manufacturer or it can be measured by the
user.
Tbm Additional time allowed for the brake monitor to
compensate for variations in normal stopping time.
Dpf Depth penetration factor. It is an added distance to allow
for how far into the protective field an object, such as a
finger or hand, can travel before being detected. Dpf is
related to the safety light curtain’s object sensitivity. Object
sensitivity is the smallest diameter object which will always
be detected anywhere in the sensing field.
European Safety Distance Formula
A safety distance must be maintained between the light curtain and the
point of danger. This safety distance helps ensure that the point of danger
can only be reached after the dangerous state of the machine has been
completely removed.
The safety distance as defined in EN ISO 13855 and EN ISO 13857
depends on:
• Stopping/run-down time of the machine or system. (The
stopping/run-down time is shown in the machine documentation
or must be determined by taking a measurement.)
• Response time of the protective device, e.g. GuardShield Type 2
(for “Response Time” see page 5).
• Reach or approach speed.
Determining Stop Time: The measurement of
stopping time (Ts) must include the stopping
times of all devices in the stop circuit. Not
including all device and control system
elements when calculating Ts will result in an
inaccurate safety distance calculation.
IMPORTANT
ATTENTION
The GuardShield Type 2 safety light curtains
must be mounted at a sufficient distance
from the pinch point or point of operation
hazard to ensure that the machine stops
before a person’s finger, hand, arm(s), or
Regardless of the calculated safety distance,
GuardShield Type 2 safety light curtains
should never be mounted closer than six
inches from the point of operation or pinch
IMPORTANT
